Kiln and related apparatus



Aug I5, 1967 M. CUVELIER 3,336,018

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Filed Aug. e, 1965 ATTORNEY ugi5, w67 M. cUvI-:LIER 3,336,018

KILN AND RELATED APPARATUS INVENTOR Michel Cuvelier FI@ e. Bymwyw ATTORNEY ug 35 i967 M. CUVELIR l 3,336,08

KILN AND RELATED APPARATUS INVENTOR Michel Cuvelier ATTORN EY United States Patent O 3,336,018 KiLN AND RELATED APPARATUS Michel Cuveiier, De! Valle, Monterrey, Nuevo Leon,

Mexico, assigner to American Radiator & Standard Sanitary Corporation, New York, NX., a corporation of Delaware Filed Aug. 6, 1965, Ser. No. 477,857 13 Claims. (Cl. 263-6) ABSTRACT F THE DISCLOSURE Ceramic ware to be fired passes through a preheat, firing, and cooling section of a kiln. The preheat section is heated by air taken from the cooling section and conducted through a passageway underneath and in heat eX- change relationship with the tiring section. The conveyor for the ceramic ware is supported from the side walls of the ring section to facilitate the construction and arrangement of the aforesaid passageway under the firing section.

This invention relates to improved kilns, coolers and dryers of the tunnel type and to a method of constructing the same.

The present invention is particularly well-suited for use with fast-tire tunnel kilns wherein the tiring cycle is usually less than 4 hours rather than 14 to 36 hours as is the case in a slow-tire kiln. The temperatures along the kiln vary as the ware being fired travels along through the kiln tunnel. The temperature rise and fall through the kiln varies from 70 F. to 2,000 F.

Kiln tunnels which have been employed heretofore have been costly to construct and have not been readily movable from place to place. There have also been problems of uneven heating. The present kiln tunnel is of sectionalized design which gives it a great deal of flexibility and permits it to be readily transported and set up in different locations. The kiln of the instant design also permits a fast change in the type of material being tired.

An object of this invention is to provide a sectionalized kiln tunnel which can be easily and quickly assembled and disassembled.

A further object of this invention is to .provide a tunnel kiln wherein duct passageways are provided to conduct heated air used for cooling the ceramic ware after it leaves the firing tunnel back, underneath the firing tunnel, to the drying section.

A further object of this invention is to provide a simplied wall construction which will permit air to be drawn downwardly behind walls of the tunnel of the cooling section, to remove heat from the iired ceramic ware before it is delivered to the discharge station without contaminating the heated air by gases from the fired ceramic ware.

A further object is to provide vertical air ducts adjacent to the cooling section of the tunnel kiln which are connected with longitudinally extending ducts positioned adjacent to the underside of the kiln to conduct the heated air to the drying section of the tunnel kiln, while minimizing the heat loss.

Other objects and features of the invention will appear as the description of the particular embodiment selected to illustrate the invention progresses. In the accompanying drawings, which form a part of this specification, like characters of reference have been applied to corresponding parts throughout the several views which make up the drawings.

FIGURE l is a plan view of the improved kiln showing the firing, cooling and drying sections.

3,336,018 Patented Aug. 15, 1967 FIGURE 2 is an elevation of the kiln taken on line 2 2 of FIG. l showing the drier which is heated by air reclamation.

FIGURE 3 shows an elevation taken on line 3 3 of FIG. 1 showing the burner portion of the kiln, which constitutes the fast preheat and tiring zone.

FIGURE 4 is an elevation taken on line 4 4 of FIG. l showing the cooling portion of the kiln.

FIGURE 5 is a vertical sectional view of the burner Zoneof the kiln taken on line 5 5 of FIGURE 3.

FIGURE 6 is a vertical sectional view of the drier section of the kiln taken on line 6 6 of FIGURE 2.

FIGURE 7 is a side elevation of the cooling zone of the kiln partially in section, taken on line 7 7 of FIG- URE 1.

FIGURE 8 is a vertical section of the cooling section of the kiln taken on line 8 8 of FIGURE 4.

FIGURE 9 is a sectional plan view of the cooling section of the kiln taken 0n line 9 9 of FIGURE 4.

Referring to FIGURES 1 to 4, I have shown how my invention can be employed with a kiln apparatus having a dryer section 10, a fast preheat and tiring or burner section 12, and a cooling section 14. Ceramic ware which is to be processed through the kiln is loaded on the conveyor 16, which travels in the direction indicated by the arrow, into the dryer 10.

This conveyor may be of any suitable design and can consist of transverse rollers forming a horizontal bed to roll material therealong.

In order to provide stability for the material being conveyed, a slab of refractory material may be employed which extends in length over several adjoining rollers and is of less width than the tunnel through which it is to be conveyed. The ceramic material which is to be fired is placed on top of such slabs. Where the ceramic material to be tired is of small size, such as wall tile, ceramic xtures called Setters may be employed into which a number of tiles or ceramic ware to be heat treated are placed to facilitate their being conveyed through the kiln tunnel.

When the ceramic ware emerges from the dryer 10', it is conveyed by the conveyor 16, around a turn and delivered into the burner section 12 of the kiln, where it is fired. The temperatures in this burner area reach 2,000 F. or more. From the burner section 12, the ceramic ware passes into the cooler section 14, where the heat is extracted from the ware. From the cooler section 14, the ceramic ware passes to the conveyor 18, around a 180 path to the discharge station 20, where the tired and cooled ceramic ware is removed and placed on either a conveyor belt 22 or on suitable trucks or pellets.

While I have shown a parallel arrangement of the burner, cooler, dryer and discharge sections, it may also be in a single straight line or it may be of a circular arrangement.

The conveyor 16, 18 may be made from any suitable conveyor material. The portions of the conveyor mechanisrn which is located inside the burner section 12, and cooler section 14 of the kiln has to Ibe made from a refractory material to withstand the high temperatures encountered in these sections.

The burner section 12 is shown in FIGURES 1, 3, 5, 6, and 7. The framework which supports `and encloses the burner section is rnore or loss similar to the framework of the cooler and drying lsections and will be described in more detail when the cooler -serction is described hereinbelow since the framework is shown in more detail in the drawing illustrating the cooler section.

The burner section is made up in sections or units 32 as shown in FIGURE 1 :so that these sections can be connected end for end and thereby equally increase or decrease the overall length yof the tiring or burner section of the kiln tunnel. The kiln tunnel area is clearly shown in FIGURES 3, 5 and 8 and consists of an upper tunnel passageway 28 and a lower passageway 30. The sides 44 of the burner section is made up of spaced angle iron uprights. An outer slab of fiber insulating material 48 is positioned in place in a manner shown in FIGURE 6. The inside sidewalls S of the kiln tunnel comprises a refractory castable material which is positioned between the outer walls 48 and the inside passageway 28, 30 of the kiln tunnel and is cast after the fiber insulating material is in place. This refractory material can be made from alumina refractory and is able to withstand the heat generated in the tunnel.

Through the sidewalls of the tunnel, burner receiving holes 3S and 40 are formed as shown in FIGURE 5. The upper and lower holes are -staggered with respect to each other to effect a uniform distribution of heat within the tunnel. A conventional burner pre-positioned in holes 3S and 40, direct a mix-ture of oxygen and fuel into the tunnel opening 28, and 30 which is burned to generate kiln firing temperatures in the tunnel.

The wall area 50, located between the upper hole 38 and the lower hole 40, has horizontally arranged holes 52 formed therein. Heat resistant shafts 54, made from refractory material extend through these holes into the ends of the larger refractory roller as shown in FIG. l The shafts 52 are all horizontally arranged in the same plane and support the rollers 56 to form a conveying surface. The end of each shaft 56, immediately adjacent the inside wall 50 of the tunnel 28, 30 is provided with a suitable ceramic or refractory bearing 59, the shafts 52 at one end only for supporting the end of the shaft: If preferred, a double bearing could be provided outside the kiln to support. The larger roller 56, which is pivotally mounted on the ends of the shafts 52, is also made from a refractory heat resistant material.

It will be thus evident that when the -shafts 52, are rotated, they will cause the rollers 56 to rotate in the same direction. Since the rollers 56 are all yarranged in a common `plan they in effect form on their upper surface a moving bed. Slabs 58 of ceramic material, which are supported on the upper surfaces of the rollers 56, are advanced rectilinearly through the tunnel 23, 30. Ceramic ware, or xtures, or setters 60 and 62 which cont-ain or support the ceramic ware which is to be fired, and which are supported yon top of the slabs 58 are advanced rectilinearly along the length of the tunnel 28 and 30 through the burner section 12 of the kiln.

The rollers 56 are so constructed that the holes 645 formed in ends of rollers 56, extend a limited distance into the rollers 56. This may be laccomplished by making the hole 64 of slightly larger diameter at the ends of the rollers 56 center portion of the hole 64. Another way of accomplishing this is to ll the center hole of the rollers 56 with a heat resistant filler such as refractory material. In this way, the center roller is prevented from moving axially aiong its length, towards either wall of the kiln tunnel 30, when it is rotated to advance the slabs 5S rectilinearly along the upper moving bed formed by the rollers 56.

It will be apparent that as the elongated slabs 58 move along the length of the tunnel 28, 30, they may sometimes move oblique-ly as they move along the rollers 56. When this `occurs the slabs 58 would normally touch the sidewalls 50 of the kiln tunnel. To avoid having the slabs 56 cause wear and gouging out `the tunnel wall-s at this point of contact, an insert 66 and 60, made from an extra hard composition of refractory material, is formed in the sidewalls 50 immediately adjacent to the paths of travel of the slabs 58. The upper portion of the kiln tunnel 2S is enclosed by ceiling slabs 70 of refractory material which are positioned to rest on insteps 72 land 74 formed in the -upper sidewalls 50 of the kiln burner section. On top of the slabs 70 may be positioned heat resistant refractory material to further insulate the tunnel area from the outside atmosphere.

The bottom bed of the kiln tunnel 76 is made from refactory material and has l or more ducts 78 and 80 formed therein and extends along the length of the kiln tunnel. These ducts are for conducting heated air lengthwise along the bottom of the tunnel and in close proximity to the underside of tunnel in a manner which is clearly shown in FIGURES 3, 5 and 8. The heated air so conducted in these ducts 78 and 80 is received from the cooling section of the kiln in a manner described hereinbelow. By conveying the hot air along the bottom of the kiln tunnel and in close proximity thereto the duct work is out of the way and the heat loss is minimized.

The lheat that is carried by the air in ducts 78 and 80 also helps to retain the heat in the kiln tunnel while retaining the heat already in the air being conducted.

While I have shown only one burner in FIG. 5 extending through the port holes 33 and 40, it will be appreciated that similar burners are mounted in each of the port holes 3S and 40 shown in FIGS. 1 `and 5 and a suitable cover plate 82 is mounted outside of each of the port holes 38 and 40.

A canopy enclosure 84 is positioned at the entrance end of the burner kiln tunnel. A funnel shaped duct 86 is connected at the entrance end of the kiln and leads into an exhaust pipe S8 as'shown in FIG. 3. Mounted in the exhaust pipe 88,. is a conventional -suitable blower (not shown) which exhausts combustion gases from the upper portion 28 of the kiln tunnel, These combustion products are exhausted to the outside atmosphere in a manner shown in FIGURE 3.

When the ceramic ware resting on top of the slabs 5S has passed through the burner section of the kiln tunnel, they pass into the cooling section 14 as shown in FIG- URES l, 4, and 8. The cooling section 14 has a bed of rollers which is similar to rollers 56 shown and described in connection with burner section shown in FIGURE 5.

The cooler is made up of individual sections as shown in FIGURES l, 4, and 8 which are joined end to end, so that the overall length of the cooler may be either increased or decreased by adding or removing sections from the cooler. This provides for a great deal of flexibility so that if the speed of travel through the kiln is increased and it is necessary to have a longer -cooling tunnel in which to remove the heat from the fired ceramic ware one merely has to add additional sections to the cooler. On the other hand if the rate of ring is decreased so that there will be a longer period of time for the fired ceramic ware to remain in the cooler section of the tunnel, then Aa shorter length Aof `cooling tunnel can be used.

It will also be apparent that the cooling section can be easily assembled and disassembled because it is sectionalized and this makes it highly portable, so that the kiln tunnel is capable of being set-up in a new area in very short time. The angle iron framework, which supports the refractory material making up the kiln is shown in detail in FIGURE 8. The angle iron framework consists `of parallel lengths of angle irons 90 and 92 which extend the length of a section. At the ends of these parallel bases 90 and 92 are corner legs 94 and 96 which extend upwardly at an angle from the bases 90 and 92. Their upper ends are joined by a horizontal length of angle iron 98. At their base, they are joined by transverse lengths of angle iron 100.

Vertical angle irons 102 and 104, extend upwardly from the transverse angle iron 98 to form the sidewall framework for the refractory material forming the side- -walls of the kiln. Across the top of the kiln is another transverse angle iron 106 which joins the upper end of vertical angle irons 102 and 104. A bracing structure is provided consisting of angle irons 108 and 110 which extend downwardly from the transverse angle iron 106 and to which it is connected at its upper end. The lower end of the angle irons 108 and 110 are formed with inwardly extending bends 112 and 114. The lower ends 116 and 118 of legs 112 and 114 are secured to the legs 94 and 96 by Welding or other suitable means as shown in FIGURE 8.

Cross studs 120 joins the vertically extending angle iron 108 to 102 while a cross stud 122, on the opposite side of the kiln, joins the vertically extending angle iron 110 to the angle iron 104, so as to form a cross brace. The sidewalls 124 and 126 of the kiln are made from an insulating fiber material. It will be appreciated that the sidewalls 124 and 126 are formed integrally in sections co-extensive with the length of each kiln section. The kiln sections 128 are shown in FIGURE 4, The outside surface of the cast walls 124 and 126 is provided with a corrugated sheet of reflective metal such as aluminum or galvanized sheet iron 12S and 139.

The inside wall surfaces 132 and 134 are made from a castable refractory concrete material and may be made U-shaped in cross section in a manner somewhat similar to that shown in the gure wherein the bottom portion 132 forms the oor of the kiln tunnel. The floor of the kiln tunnel, which is made of castable concrete, is supported on the transverse angle irons 44, and has a pair of ducts 78 and 80 extending lengthwise along the length of the kiln in a manner similar to that shown in FIGURE 5.

Suitable stanchions 136 and 138 shown in FIGURES 8 and 9 extend upwardly and loutwardly at spaced intervals as shown in FIGURE 9. Suitable slots 140, 142, 144 and 146 are formed in each stanchion and extend up and down so that when a very hard sheet or slab of thin refractory material 147 is lowered downwardly in these slots 140, 142, 144, 146 they form downwardly extending air passageways, 148, 150, 152, 154. The thickness of the sheet 147 should preferably be between 1/2 and 34 in thickness.

The cooling section shown in FIGURE 9 shows a series of these walls and a series lof such vertically extending ducts. For brevity only one end has been described since the other end is constructed in a similar manner. Due to the rotary motion imported to the ceramic conveying rollers 56 the tile Setters or ceramic ware 60 and 62 is moved along, in the direction indicated by the arrow, as they rest on their respective ceramic supporting slabs 58. The heat radiated from the red ceramic ware is conducted through the vertically extending very hard sheets 147 so that as air is drawn downwardly through a vertically extending duct 148 to 154, the air will pick up heat as it passes into the horizontally extended ducts 78 and 80 which are located underneath and extend along the length of the cooler section of the kiln.

The heated gas which enters the ducts 78 and 80 formed in the bed 132 of the cooler sections and bed 76 of the burner section will be delivered to a header duct 156 (FIGURE 3). From there the gas passes into a duct 158 and then into a centrifugal or squirrel cage blower 160 from which it is discharged outwardly into a duct 162 into a header 164 (FIGURE l). The header 164 is mounted on top of the discharge end of the dryer section as shown in FIGURES l and 2. The heated air coming from the cooler 14 through ducts '78 and 81) in this manner then passes through the dryer 10 in a direction transverse to the direction which ceramic ware moves through the dryer 10. The header 166, shown in FIGURE 2, is mounted at the opposite end of the dryer 10, and removes and extracts air from the dryer section after it has passed therethrough and discharges said air through duct 168 which is connected with a conventional blower which exhausts same to the outside atmosphere.

The dryer portion of the kiln is also sectionalized and consists, in the embodiment used to illustrate the invention in FIGURE 2 of six sections 170. It will be evident that these individual sections can be readily assembled and disassembled and a number of sections can be either increased or decreased depending upon the drying requirement of the ceramic ware being processed, and the speed of operation of the kiln.

Since the ceramic ware to be dried at this stage does not yhave any material amount of heat therein, it is not necessary for the conveyor mechanism which moves the ceramic ware through the tunnel to be made of a heat resisting material. For example, metal rollers of nonrefractory material could be employed to convey the material in a manner similar to that shown in FIGURES 7 and 9. On the other hand, a chain conveyor mechanism could be also readily employed for this purpose. When the material has passed through the dryer 10, it is then delivered on the connecting conveyor 16. Here again the connecting conveyor may be of any conventional type of construction and it does not have to be of heat resisting material. It is only when the ceramic ware enters into the burner section of the kiln that it is necessary to have and employ a conveyor mechanism which is of a heat resisting material.

An adjustable closure (notshown) can be mounted at the entrance end of the preheat section of kiln 12 and at the discharge end of the cooler 14, and at the entrance and discharge ends of the dryer 10, so as -t-o restrict the air therein to predetermined paths of travel within the tunnel area. By the time the tired ceramic ware has been cooled down to .approximate room temperature it has reached the end of the cooler 14, and is discharged onto a conveyor 14, which may be of a conventional construction. The conveyor 14, `delivers the discharged material to the unloading station 2.0, for transfer to a conveyor belt 22, pallets or conventional hauling trucks.

It will be apparent from the foregoing inscription that I have described and illustrated a sectionalized kiln which is highly versatile in that it can be used for ring one type of ceramic ware at one time and quickly converted and adjusted to re ceramic ware `of another type. Since the items being red pass through the kiln seri-ally rather than in compact batches the change from one type of material to another type of material consists primarily of temperature and speed adjustments.

The invention hereinabove described may, therefore, be varied in construction within the scope of the claims, for the particular device selected to illustrate the invention is but one of many possible embodiments of the same. The invention, therefore, is not to be restricted to the precise details of the structure shown and described.

What is claimed is:

1. Apparatus for ring ceramic ware such as tile, comprising a drying tunnel, a firing tunnel, a cooling tunnel,

a conveyor for moving said ceramic ware through said tunnels, said ring tunnel having a rbottom wall and side walls with the latter having means to support said conveyor above the bottom wall to render the latter non-load bearing, air ducts in said cooling tunnel for removing heat from tired ceramic ware, duct work connected -to said airducts and extending along and immediately adjacent and under said tiring tunnel to preserve the heatA in the air conveyed through the duct work while leading said air into said drying tunnel for drying ceramic ware before it enters into said firing tunnel.

2. Apparatus for firing ceramic ware comprising, a drying section, a tiring section, and a cooling section, all having tunnel areas extending along the length thereof, an endless conveyor for moving ceramic ware through the drying section, the firing section and the cooling section from a loading station to an unloading station, said firing and cooling sections each having a bottom Wall and side walls with the latter having means to support said conveyor above the bottom walls to render the latter non-load bearing and means for transferring heat from the cooling section to the drying section by conducting heat carrying air in longitudinal passageways incorporated in the bottom wall and positioned directly below the tunnel areas of said cooling and tiring sections, to effect a cooling and a drying in said respective sections.

3. Apparatus for firing ceramic ware comprising, a drying section, a tiring section, and a cooling section, all having tunnel areas extending along the length thereof, an endless conveyor for moving ceramic ware through the drying section, the ring section and the cooling section from a loading station to an unloading station, said tiring section having a bottom wall and side walls with the latter having means to support said conveyor above the bottom wall to render the latter non-load bearing, and means for transferring heat from the cooling section to the drying section by conducting heat carrying air in longitudinal passageways incorporated in the bottom wall and positioned directly Abelow and in heat transfer relationship with the tunnel area of said firing section, and hardened ledges of high temperature ceramic material positioned adjacent the path of travel of the ceramic ware passing through said tiring tunnel to prevent the sides of the latter from being gouged as the ware is advanced through said tunnel.

4. Apparatus for firing ceramic ware according to claim 9 wherein said cooling section has a bottom wall and hardened ledges of high temperature ceramic material positioned adjacent the path of travel of the ceramic ware passing through said cooling tunnel to prevent the sides of said tunnel being gouged as the ware is advanced through said tunnel.

5. Apparatus for tiring ceramic ware comprising, a tiring tunnel having a bottom wall and side walls, a conveyor for moving ceramic ware to be tired through said tunnel, said side walls having means to support the conveyor above said bottom wall thereby to render the latter non-load bearing, a cooling tunnel connected to said tiring tunnel for removing the heat from the ceramic ware, a longitudinal passageway incorporated in said bottom wall and extending along the underside of the tiring tunnel whereby heat transfer may be effected between the tiring tunnel and the underlying longitudinal passageway through said non-load bearing bottom wall, a drying tunnel through which lceramic ware to be fired is conveyed, and means for directing the heated air removed from the cooling tunnel through said longitudinal passageway to said i drying tunnel.

6, Apparatus for firing ceramic ware according to claim further comprising burner means disposed in the side walls of said tiring tunnel, at least one of said -burner means being disposed at an elevation between the conveyor and said bottom wall.

7. Apparatus according to claim S wherein said conveyor comprises a plurality of heat refractory and heat resist-ant shafts extending into the side walls of the ring tunnel and spaced from said bottom wall.

8. Apparatus according to claim '7 further comprising heat resistant bearings in said side walls rotatably supporting said shafts.

9. Apparatus according to claim 7 further comprising heat resisted rollers carried on said shafts to define a conveying surface, and slabs of ceramic support material carried on the upper surface of said rollers and adapted to lll be advanced rectilinearly through said tiring tunnel, said ceramic ware being carried on said slabs.

1t?. Apparatus for tiring ceramic ware according to claim 5 wherein there is provided a hollow wall construction forming the sidewalls of said cooling tunnel, the inside side walls of said cooling tunnel consisting of hardened refractory material which is 1/2 to 3,/4 inch in thickness and is inserted between the tunnel path of the ceramic ware and the outside walls of said cooling tunnel to facilitate a transfer of heat from the ceramic ware through refractory material to the air passing downwardly through said hollow walls.

11. Apparatus for tiring ceramic ware according to claim 5 wherein said cooling tunnel has outer walls of refractory material, upright stanchions positioned at spaced intervals along opposite outer walls, said stanchions having vertical slots formed therein for receiving thin plates of refractory material to form a vertical duct between said outer walls and said plates, elongated horizontally extending air passageways extending along the length and underneath of said cooling tunnel area and air passageways interconnecting the vertical duct with said elongated horizontally extending air passageways to remove heat from fired ceramic ware.

12. Apparatus for firing ceramic ware comprising, a firing tunnel having a bottom wall and side walls, a conveyor having rollers on which the ceramic ware to be tired is moved through said tunnel, said side walls having bearing means to support said rollers above said bottom wall thereby to render the latter non-load bearing, a cooling tunnel connected to said tiring tunnel for removing the heat from the ceramic ware, a longitudinal passageway incorporated in said bottom wall and extending along the underside of the firing tunnel whereby heat transfer may be effected between the tiring tunnel and the underlying longitudinal passageway through said non-load bearing bottom wall, a drying tunnel through which ceramic Ware to be tired is conveyed, an-d means for directing the heated air removed from the cooling tunnel through said longitudinal passageway to said drying tunnel.

13. Apparatus according to claim i2 further comprising burner means in said firing tunnel disposed above and below said conveyor rollers.

References Cited UNITED STATES PATENTS 1,403,734 1/l922 Booth 25-142 X 1,471,875 lil/1923 Witte 25-142 1,539,653 5/1925 Duckham 25-142 1,584,241 5/1926 Mulholland 263-8 1,854,452 4/1932 Cramer 263-44 X 1,858,008 5/1932 Forse et al. 25-142 2,856,172. 10/1958 Kautz 263-6 FREDERICK L. MATTESON, JR., Primary Examiner.

D. A. TAMBURRO, Assistant Exdminer. 

1. APPARATUS FOR FIRING CERAMIC WARE SUCH AS TILE, COMPRISING A DRYING TUNNEL, A FIRING TUNNEL, A COOLING TUNNEL, A CONVEYOR FOR MOVING SAID CERAMIC WARE THROUGH SAID TUNNELS, SAID FIRING TUNNEL HAVING A BOTTOM WALL AND SIDE WALLS WITH THE LAYER HAVING MEANS TO SUPPORT SAID CONVEYOR ABOVE THE BOTTOM WALL TO RENDER THE LATTER NON-LOAD BEARING, AIR DUCTS IN SAID COOLING TUNNEL FOR REMOVING HEAT FROM FIRED CERAMIC WARE, DUCT WORK CONNECTED TO SAID AIR DUCTS AND EXTENDING ALONG AND IMMEDIATELY ADJACENT AND UNDER SAID FIRING TUNNEL TO PRESERVE THE HEAT IN THE AIR CONVEYED THROUGH THE DUCT WORK WHILE LEADING SAID AIR INTO SAID DRYING TUNNEL FOR DRYING CERAMIC WARE BEFORE IT ENTERS INTO SAID FIRING TUNNEL. 